This invention relates to transparent thermoplastic compositions having improved processability, improved mar resistance and reduced friction. More particularly, it relates to such compositions containing a transparent thermoplastic selected from polystyrene, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, acrylate polymers or polycarbonate, the compositions being modified by the addition of a fluid organosiloxane copolymer.
Minor amounts of polydimethylsiloxane fluids are often admixed with thermoplastics to provide the thermoplastic with beneficial properties such as reduced friction and wear, improved mar resistance and improved processability. Many such internally lubricated thermoplastic compositions have achieved considerable commercial success due to the improved properties obtained with minimal cost.
However, admixtures of polydimethylsiloxane fluids and thermoplastic polymers are not useful when transparent thermoplastic objects are desired because of the incompatibility of the polydimethylsiloxane with thermoplastic polymers. This incompatibility results in admixtures that are opaque or milky white in appearance even at very low levels of polydimethylsiloxane. For example, U.S. Pat. No. 3,087,908 discloses that polydimethylsiloxane gives detectable haze in polycarbonate films at concentrations as low as 200 parts per million with significant haze occurring at siloxane concentrations above 400 parts per million. While these low concentrations may provide some enhancement of film forming properties, they are not sufficient to provide the major processing and wear benefits of internal lubrication. As disclosed by U.S. Pat. No. 2,999,835 such benefits are obtained in polycarbonates at siloxane concentrations above 0.1 weight percent or even preferably at 1 weight percent or above. Similar results have been observed with other thermoplastic polymers.
It is a purpose of the present invention to provide internally lubricated transparent thermoplastic compositions. Further, it is a purpose of the present invention to provide an organosiloxane that is compatible with thermoplastic polymers at concentrations appropriate for effective internal lubrication. Still another purpose of the invention is to provide a compatible organosiloxane that can provide internal lubrication in thermoplastic polymers comparable to that obtained with polydimethylsiloxanes.